In hydraulic-elastomeric mounts such as used for mounting an internal combustion engine in a motor vehicle, a hydraulic damping decoupler can be employed to eliminate undesirable hydraulic damping at certain small vibratory amplitudes and low frequencies and thereby better isolate the vibrations of the engine under these conditions. Such decouplers are normally reciprocating devices which are mounted on a partition separating the two orifice connected chambers of the mount and operate to effect alternating volume change in the chambers so as to not force flow through the orifice and thereby eliminate damping in this mode. While the performance of such decouplers has proven generally satisfactory, it has been found that they typically slap against flat partition surfaces determining the limits of their movement and that such slaps can produce a discernible noise that is objectionable.